Recent trends in the telecommunications industry towards unified communications emphasize the need for converged networks to deliver acceptable quality of service (QoS) for different types of applications with varying QoS needs. Real-time applications such as video streaming or voice over IP (VoIP) demand strict QoS guarantees from the underlying data network. Understanding the network behavior at all stages of the deployment of such applications is critical for their performance. For example, at the pre-deployment stage, it is necessary to assess whether the network can deliver the required QoS and more importantly which parts of the network fail to do so. After deployment, monitoring the performance of the network is necessary for maintaining acceptable QoS levels.
Numerous network monitoring and analysis systems are known in the art. See, for example, U.S. Patent Application Publication No. 2005/0053009, entitled “Method and Apparatus for Automatic Determination of Performance Problem Locations in a Network,” which discloses root cause analysis techniques for determining the particular locations associated with performance problems in a network comprising a plurality of endpoint devices.
Network monitoring and analysis systems often collect low-level network measurements, such as delay, jitter and packet loss, in an effort to understand how network conditions will affect real-time applications. However, such low-level network measurements can be difficult to interpret in terms of their impact on perceived quality of a received stream. For this reason, the low-level measurements are often supplemented by an estimated Mean Opinion Score (MOS) that conveys the overall perceived quality of a received stream on a scale from 1 to 5. See ITU-T Recommendation P.800, “Methods for subjective determination of transmission quality.” Another known perceived quality estimation technique utilizes the E-model described in ITU-T Recommendation 0.107, “The E-model, a computational model for use in transmission planning.” The E-model uses low-level network measurements to compute a scalar value known as an R-factor that can range from 0 to 100 and can be mapped to an estimated MOS. In the case of VoIP applications, a conversational estimated MOS may be used that characterizes the concurrent perceived quality of received streams in two directions.
A significant drawback of conventional approaches based on the above-noted estimated MOS and the E-model is that these approaches convey only a very simplified description of the experienced quality. Accordingly, these techniques do not allow network engineers to reproduce and experience for themselves the particular quality problems reported by users of network applications, which can make the problems very difficult to analyze and correct. This is particularly true in situations in which the quality problems are attributable to rare or transient network conditions.